An X-ray CT apparatus irradiates X-rays from the vicinity of an object, and generates a distribution of an X-ray absorption coefficient of the object as an image on the basis of projection data acquired at a plurality of projection angles. As an X-ray irradiation dose becomes larger, an image with less noise can be acquired, and thus image quality is improved. On the other hand, in recent years, an influence of exposure to X-rays on the human body has become problematic, and thus techniques have been actively examined in which image quality for a doctor to perform diagnosis is obtained even in a case where an X-ray irradiation dose is minimized. As one of the techniques, an automatic exposure control (AEC) technique of adjusting an X-ray irradiation dose during scanning according to information such as a size of an object or a scanning part, and image quality desired by an operator is widely known (PTL 1). As an index of the X-ray irradiation dose which is controlled in the AEC technique, a tube current-time product which is a product of a current (hereinafter, referred to as a tube current) applied to an X-ray tube and time (hereinafter, referred to as scan time) for a scanner to rotate one time is generally used.